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32 Cards in this Set

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  • Back
Advantage of eddy current?
fast, may be automated, no post cleaning, equip light and portable, sensitive to small surface cracks, wide band of applications.
disadvantage if eddy current?
only works on metal, electrical and magnetic interference may cause problems, highly trained personnel are required, and affected by numerious variables.
What is the movement of electrical charge?
Current Flow (electrons)
Free electrons are driven by?
Electric field.
how many free electrons due insulators have?
None
Metals have how many free electrons?
many (conductor)
In a wire electrons collied with the atoms making up what?
The conductor
The collisions from the electrons colliding with the atoms causes a loss of what?
energy loss through heat
The collision of electrons and atoms also limits current flow this is called?
resistivity
Conductivity is thge opposite of what?
resistivity
When a treaveling elctron has a force act upon it in a sideways manner this is defined as?
magnetic field
like an electric current a magnetic field can do what?
exert a force on electrons producing current flow
When a magnet is moved past a conductor what two things happen?
Current is induced and the current produces its own magnetic field (secondary)

This is known as lenz's law
The magnetic field arounda straight wire is weak unless what?
tremendous amouns of current are applied.
By forming the wire in a coil it will produce a strong magnetic field with what?
far less current.
The strength of the field at the surface depends on what?
The size and shape of the coil, amount of current through coil and the distance from coil to the inspected artical.
What type of current do eddy current machines use?
AC
What is ipedence?
opposes current flow by causing impeding of the wire. That heat is energy loss to the atmosphere.
what is reactance?
opposes changes in current flow by causing energy to be stored in the field around the wire.
what are the two types of reactance?
inductive and copasitive. But compasitive is very small and not considered.
resistance and reactance combined to form what?
impedance.
when resistance is isolated from reactance is what?
the ratio of an applied voltage to current flowing through a circut.
reactance when isolated from resistance is the opposition to?
the flow of AC current caused by inductance in a circuit. Current lags voltage by 90 degrees.
conductivity is what?
a measure of ease with whick electrons can flow through a meterial. Also the opposite of resistivity.
conductivity is based on what as far as standards?
IACS international annealed copper standard.
What are some things that effect the conductivity of the eddy currents?
distribution and intensity are stronly effected by conductivity.

magnituded of eddy imediatly below the surface is depedent on the conductivity of the part

High conductivity equals strong eddy current

strong eddy currents form a strong secondary magnetic field which opposes field.
penetration in materials is better in what type of conductor?
poor
the closer the coil is to the part the what?
the stronger the eddy currents will be
Geometry is what and how does it effect eddy currents?
The variation in parts.

Thickness changes afect impedance by containing mor or less of the iduced field and mor or less eddy currents will be generated

edges, corner and radii all disrupt eddy current that intercept them thus changing current distribution and magnitude.
Discontiunuities effect eddy current how?
Deep flaws give more response

and shallow flaws give less
Frequency
Represents the number of cycles per sec of AC used to establish a magnetic field in a part.
How does tempreture play a role?
effects both electical conductivity and material properties.

High temp will decrease electrical conductivity.

gives unstable readings.